The sensitivity of high resolution respirometry (HRR) has made it possible to carry out reliable measurements of oxygen consumption even in blood cells, opening up new scenarios for the mitochondrial function / dysfunction in health conditions, but also to study the pathophysiology of many diseases or the effects of effects of interventions. However, the premises of all this must be sought in the validation and comparison of the preparatory procedures, from blood collection to cell purification and in the protocols adopted for the analysis. Here are presented the procedures adopted for peripheral blood mononuclear cells (PBMC) [1,2] and for platelets (PLT) [3, 4], also in relation to other laboratories participating in WG4. Crucial points emerged and the various solutions adopted will be highlighted. We found that in the isolation of cells different approaches can be used, and the results are not always divergent.